1. Field of the Invention
The invention is directed to a mine roof support fixture to develop an effective load control monitor to respond to movement of the roof material or respond as a rigid support or a yieldable support.
2. Description of the Prior Art
It is known that in the creation of underground passages geologic forces are released which cause strains in the earth surrounding the passage, and that the strain is reflected by movements of the geologic material, especially in the roof of such passage. Means for resisting the forces to re-establish balance are such that they retard movement of the geologic material, not only in the roof, but around the passage and such means can be in several different forms. An early form of roof bolt is disclosed in Ralson U.S. Pat. No. 2,850,937 on Sep. 9, 1958. In this disclosure, the roof bolt imbodies indicated means which can be seen and which convey information regarding whether or not the roof bolt is supporting its desired load in the mine roof.
References also made to Emery U.S. Pat. No. 3,226,934 of Jan. 4, 1966, Reusser U.S. Pat. No. 3,478,523 of Nov. 18, 1969, directed to rock bolts having a load bearing plate for use in mine roof support. Many other patents exist on roof bolt fixtures and on cable anchored fixtures which include Scott U.S. Pat. No. 4,378,180 of Mar. 29, 1983. The prior art also includes Askey et al U.S. Pat. No. 3,797,254 of Mar. 19, 1974.
In certain roof support fixtures the design is directed to overcoming the problems of placing long bolts in low seam heights which requires coupling of the parts of the fixture and a weakening of the fixture due to the couplings. The couplings also increase the cost and the thread of the rod produce stress concentrations Holes into which these type roof fixtures are placed are larger to accomodate the oversized couplings. A cable-type roof bolt, for example a 7-strand cable, 5/8 inch diameter or 1/2 inch diameter, can readily be placed in a one inch diameter hole in a low seam by bending the cable in order to obtain insertion, thus eliminating couplings. A difficulty with this cable support is it is hard to make an attachment to the end which will allow rotation of the cable upon insertion and for retaining the roof plate.